When modern electrophotographic printers were first introduced, substantial problems were experienced with the paper feed and handling mechanisms. Over the years, such mechanisms, especially those designed to handle flat sheet stock, have greatly improved and now provide reliable service. Such sheet feed mechanisms generally remove a single sheet from a stack by grabbing the topmost sheet and feeding it into the printer mechanism. Using a top feed system enables the user to add a single sheet to the stack and to have it fed upon the next print cycle. Thus, if it is desired to insert a letterhead sheet, it merely needs to be placed at the top of the stack. Were the sheets fed from the bottom, the insertion of a single sheet would be substantially more inconvenient.
Similar advances have not been experienced with envelope feeders. The thickness and shape of envelopes generally dictates that envelope feeders feed from the bottom of an envelope stack. This has prevented the integration of sheet/envelope feeders.
The prior art has approached the problem of envelope feeding mainly via two routes. The first required that all of the sheet stock be removed from the sheet feeder and a single envelope fed therethrough. Systems using this technique were generally unable to handle, automatically, a series of envelopes. The second required provision of an entirely separate envelope-feeding mechanism that was insertable into the printer body. Within the printer body there was a set of feed rolls which would grab the envelope and then feed it into the printer body. This latter technique required the addition of additional mechanisms and circuits to the printer, which often went unused if the user did not purchase an optional envelope feeder. This resulted in an increase in the cost of the printer to all customers, as it was uneconomical to manufacture a special printer, particularly for customers who wanted the optional envelope feeders.
Accordingly, it is an object of this invention to provide an improved, automatic, envelope/sheet feed mechanism.
It is another object of this invention to provide an improved envelope/sheet feed mechanism particularly adapted for inclusion in a non-impact printer.
It is still another object of this invention to provide a combined envelope/sheet feed mechanism which requires little modification to a printer already having the capability to top-feed sheets.